语法讲解：名词性从句

名词性从句

名词性从句相当于名词，可分别作主句的主语、表语、宾语和同位语。因此，名词性从句厅分为主语从句、表语从句、宾语从句和同位从句。

（一）引导名词性从句的连接词

1、连接代词：who, whose, whom, what, which。有词义，在从句中担任成分，如主语、表语、宾语、或定语等。

2、连接副词：when, where, why, how。有词义，在从句中担任成分，作状语。

3、连接词：that, whether, if, as if。that 无词义，在从句中不担任成分，有时可省略；if (whether), as if虽有词义，但在从句中不担任成分。

不可省略的连词：

a. 介词后的连词

b. 引导主语从句和同位语从句的连词不可省略。

That she was chosen made us very happy.

We heard the news that our team had won.

比较：whether与if 均为"是否"的意思。但在下列情况下，whether 不能被if 取代：

a. whether引导主语从句并在句首

b. 引导表语从句

c. whether从句作介词宾语

d. 从句后有"or not" Whether he will come is not clear.

大部分连接词引导的主语从句都可以置于句末，用it充当形式主语。

It is not important who will go.

It is still unknown which team will win the match.

（二）主语从句

1、主语从句在复合句作主语。

e.g. Who will go is not important.

2、用it作形式主语，主语从句放在句末。

e.g. It doesn’t matter so much whether you will come or not.

用it作形式主语的that-从句有以下四种不同的搭配关系：

a. It + be +形容词+ that-从句

It is necessary that…有必要……

It is important that…重要的是……

It is obvious that…很明显……

b. It + be + -ed 分词+ that-从句

It is believed that…人们相信……

It is known to all that…从所周知……

It has been decided that…已决定……

c. It + be +名词+ that-从句

It is common knowledge that………是常识

It is a surprise that…令人惊奇的是……

It is a fact that…事实是……

d. It +不及物动词+ that-分句

It appears that…似乎……

It happens that…碰巧……

It occurred to me that…我突然想起……

3、that引导主语从句时，不能省略。

e.g. That he suddenly fell ill last week made us surprised.

注: 1）what = the thing which；whatever = anything

What you want has been sent here.

Whatever you want makes no difference to me.

2) who= the person that whoever= anyone who

（错）Who breaks the law will be punished.

（错）Whoever robbed the bank is not clear.

（对）Whoever breaks the law will be punished.

（对）Who robbed the bank is not clear.

（三）表语从句

1、表语从句在复合句中作表语，位于系动词之后。

e.g. The question was who could go there.

2、引导表语从句的连接词that有时可省去。

e.g. My idea is (that) we can get more comrades to help in the work.

（四）宾语从句

1、宾语从句在复合句中作宾语。引导宾语从句的连词that一般可省略。

e.g. I hope (that) everything is all right.

2、介词之后的宾语从句，不可用which或if连接，要分别用what或whether。

e.g. I’m interested in whether you’ve finished the work..

I’m interested in what you’ve said.

3、whether与if都可以引导宾语从句，常可互换。但下面情况不能互换。

①宾语从句是否定句时，只用if，不用whether。

e.g. I wonder if it doesn’t rain.

②用if 会引起误解，就要用whether。

e.g. Please let me know whether you want to go.（此句如果把whether改成if，容易当成条件句理解）

③宾语从句中的whether 与or not直接连用，就不能换成if；不直接连用，可换。

e.g. I don’t know whether or not the report is true.

I don’t know whether/ if the report is true or not.

④介词后的宾语从句要用whether引导。whether 可与不定式连用。whether也可引导主语从句、表语从句、同位语从句，还可引导让步状语从句，以上均不能换成if。但引导条件从句时，只能用if，而不能用whether。

e.g. It depends on whether we have enough time.

They don’t know whether to go there.

Please come to see me if you have time.

（五）同位语从句